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SAN DIEGO -- A free iPhone social networking application called Bump, which lets users quickly share personal contact information and photos, created a buzz at the CTIA International wireless conference.

Bump, from Bump Technologies Inc. in Mountain View, Calif., first appeared in March, and was distinguished as the billionth download from Apple Inc.'s App Store. Thanks to that achievement, it was prominently featured in an iPhone TV ad and drew the attention of iPhone users -- and six months later, the level of attention seems to have multiplied.

Bump aroused the curiosity of analysts and technology buffs at CTIA partly because of the way it uses AT&T Inc.'s network and the iPhone's built-in GPS functionality and sensors to help users share their contact information.

The Bump allows two users who have loaded the app onto their iPhones clench their devices in their hands and then tap their hands together in a gentle fist bump to begin the exchange of information stored in each phone.

A bartender at a CTIA party who noticed mobile phone executives playing with phones in the crowd remarked that Bump is his favorite iPhone app. "I don't know how it works, but you just bump another person, and it works," he said.

So, how does it work?

IDC analyst Scott Ellison said most Bump users mistakenly believe the device transmits the data over the air via Bluetooth or an infrared signal. However, the app actually relies on AT&T's 3G cellular or EDGE networks or Wi-Fi to transmit the data between phones.

The Bump FAQ gives more details about how the phones identify each other and how each knows that the other is ready to transmit data.

According to the FAQ, the Bump app runs on the iPhone and a matching algorithm runs on a server in the cloud. The app on the phone uses the sensors on the phone to "feel" the bump, sending that information to the server. The algorithm responds to bumps from phones globally and pairs up phones that "feel" the same bump, and it then routes the contact information between the two phones in the pair. The process takes less than 10 seconds.

Ellison said that Bump relies on GPS to give the location of each phone, but it also uses the iPhone's accelerometer, which detects movement.

The FAQ says that if two pairs of users bump their phones at the same time and in close proximity to each other -- at a crowded party, for example -- and the server can't identify the specific matches, the pairs will be asked to bump again.

The communications between the phones and the server are encrypted for greater security. Once a bump is made, the server will find the two phones that felt the bump and then ask each one to transmit the contact information, but nothing else, the FAQ says. If both users confirm that the match is correct, the information is sent to the other party.

Bump Technologies said that it plans to keep the basic version free for the "entire foreseeable future" and that it is working to make the app available for other smartphones equipped with sensing technologies "in the near future."

The Apple App Store includes a variety of customer reviews that show how Bump is used. One comment, by someone identified as Paddledave, says the app is "great if you are in a bar and too drunk to trade contacts." Another by a user dubbed cwinfoseeker says, "it's cool but it would be way better if u could bump music and apps with ur friends."

Ellison said the Bump is "very, very snazzy" and is a good example of the capabilities of emerging mobile technologies. But he also said he foresees a time when "bump brawls" could break out at parties, and he's not completely kidding. "What if somebody basically says 'Hey baby' to a woman [with a bump], and her husband or boyfriend is standing nearby?" he said.